Hey all! THanks for reading.

I recently had my family's shop (about an hour away) do some work on my 1984 300D. It got a new carrier bearing, u-joint, and some front end work.

And now it has a rattle that is shaking through the driveshaft tunnel and in the rear! My brother reported that it had a vibration, but that one day he took it out with a mind to figure out what was going on, and the vibration just went away. Indeed, when I drove off with it there was little vibration if any until I got back to my city and had to start from a stop light. Then it shook like hell! That vibration came and went as I drove it around town for work while trying to figure out what to do next.

So I searched and learned more than I ever wanted to know about driveshafts, and then put the rear wheels on stands and started looking around under the car.

Here's the thing - everything appears indexed - front and rear flanges across the flex discs to differential/tranny flanges. However, the factory = on the u-joint knuckle is not aligned with the - just past the sleeve nut.

Now, I've also seen it said in these parts that the flanges/yokes need to be aligned front to rear - I assume that means that if the rear shaft flange is pointing down then the front shaft flange should also be pointing down. Is this correct? Or does it matter. The shaft flanges DO "point down" together, and appear to be aligned through the spline and not one notch off to either direction.

My theory is that perhaps the u-joint knuckles didn't go back the same way they were originally. Like if one was numbered 1 & 3, and the other was 2 & 4, then they got switched from 1/2/3/4 to 1/4/3/2. Make sense?

Except, when I rotate it all around and visualize how changing that would affect things, I can tell that then the flanges wouldn't line up. And, I recognize that what would have been flipped would be relatively small piece of the overall shaft - u-joint knuckle to the splines.

So, the factory marks are not aligned, but the majority of the shaft is aligned. The factory marks are maybe at 12 o'clock and 4 o'clock.

My brother was not aware of the factory marks. And this car was made in January 1984, so could it even be possible it was during the time that MB had cast them but wasn't using them?

Also they (in trying to cure rattle) replaced the transmission mount, and I replaced the differential mount after getting it back. I didn't drive it prior to the transmission mount replacement, but the differential mount replacement did soften the rattle. However, around this time, the rattle stabilized into consistent onset around 38 mph and being the worse slightly faster - maybe by 42 mph, then smoothing out quite a bit with speeding up, but not all the way disappearing.

Tonight I looked everything over again and replaced the flex-discs (adding my own new index marks). The old MB "transmission" flex disc had a crack that was visible when moving the driveshaft around. The rear one seamed fine if maybe a little "alligatoring" on the surface, as though it had been clear-coated and that had crackled. Driving after flex disc replacement revealed improved performance, but still vibration at the same speeds.

Both they and I have done the loosening, rolling, retightening procedure for sleeve nut, trans mount, and carrier bearing.

Please advise! Junk yard drive shaft is starting to sound appealing.

My brother suspected a half-axle issue. I replaced both of those earlier this year with CVJ rebuilds after a catastrophic failure. However, this vibration did not appear after THAT repair!

I did discover that the driverside rear wheel hub has a touch of play in it, which seems to have gotten worse since my initial drivetrain inspection. It once simply made a "tink" sound when I yanked on it, but now has a little bit of jiggle. Could this cause a vibration up through the driveshaft that would rattle the change in my center console?

Sorry if this is TMI - but I wanted you to know all from the onset! Thanks again for any help!

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting